1. Field of the Invention
This invention relates generally to the field of multimedia systems. More particularly, the invention relates to a improved multimedia system for compressing and decompressing multimedia content and data using a mass storage device.
2. Description of the Related Art
A prior art system for receiving and storing an analog multimedia signal is illustrated in FIG. 1a. As illustrated a selector 107 is used to choose between either a baseband video input signal 102 or a modulated input signal 101 (converted to baseband via a tuner module 105). A digitizer/decoder module is 110 performs any necessary decoding of the analog signal and converts the analog signal to a digital signal (e.g., in a standard digital format such as CCIR-601 or CCIR-656 established by the International Radio Consultative Committee).
An MPEG-2 compression module 115 compresses the raw digital signal in order to conserve bandwidth and/or storage space on the mass storage device 120 (on which the digital data will be stored). Using the MPEG-2 compression algorithm, the MPEG-2 compression module 115 is capable of compressing the raw digital signal by a factor of between 20:1 and 50:1 with an acceptable loss in video image quality. However, in order to compress a standard television signal (e.g., NTSC, PAL, SECAM) in real-time, the MPEG-2 compression module 115 requires approximately 8 Mbytes of RAM 116 (typically Synchronous Dynamic RAM or “SDRAM”). Similarly, after the video data has been compressed and stored on the mass storage device 120, the prior art system uses an MPEG-2 decompression module 130 and approximately another 8 Mbytes of memory 116 to decompress the video signal before it can be rendered by a television 135.
Prior art systems may also utilize a main memory 126 for storing instructions and data and a central processing unit (“CPU”) 125 for executing the instructions and data. For example, CPU may provide a graphical user interface displayed on the television, allowing the user to select certain television or audio programs for playback and/or storage on the mass storage device 120.
A prior art system for receiving and storing digital multimedia content is illustrated in FIG. 1b. Although illustrated separately from the analog signal of FIG. 1a, it should be noted that certain prior art systems employ components from both the analog system of FIG. 1a and the digital system from FIG. 1b (e.g., digital cable boxes which must support legacy analog cable signals).
As illustrated, the incoming digital signal 103 is initially processed by a quadrature amplitude modulation (“QAM”) demodulation module 150 followed by a conditional access (“CA”) module 160 (both of which are well known in the art) to extract the underlying digital content. As indicated in FIG. 1b, the digital content is typically an MPEG-2 multimedia stream with a compression ratio selected by the cable TV or satellite company broadcasting the signal. The MPEG-2 data is stored on the mass storage device 120 from which it is read and decompressed by an MPEG-2 decompression module 130 (typically using another 8 Mbytes of RAM) before being transmitted to the television display 135.
One problem associated with the foregoing systems is that the memory and compression logic required to compress and decompress multimedia content in real time represents a significant cost to manufacturers. For example, if 8 Mbytes of SDRAM costs approximately $8.00 and each of the compression and decompression modules cost approximately $20.00 (currently fair estimates), then the system illustrated in FIG. 1a would require $56.00 to perform the compression/decompression functions for a single multimedia stream. Moreover, considering the fact that many of these systems include support for multiple multimedia streams (e.g., two analog streams and two digital streams), the per-unit cost required to perform these functions becomes quite significant.
Another problem with the digital system illustrated in FIG. 1b is that it does not allow users to select a particular compression level for storing multimedia content on the mass storage device 120. As mentioned above, the compression ratio for the MPEG-2 data stream 170 illustrated in FIG. 1b is selected by the digital content broadcaster (e.g., digital cable, satellite, Webcaster, . . . etc). In many cases, however, users would be satisfied with a slightly lower level of video quality if it would result in a significantly higher MPEG-2 compression ratio (and therefore more available storage space on the mass storage device).
Accordingly, what is needed is a more efficient means for compressing and decompressing multimedia content on a multimedia storage and playback device. What is also needed is an apparatus and method which will allow users to select a compression ratio and/or compression type suitable to their needs (e.g., based on a minimum level of quality given the capabilities of their mass storage devices).